bool isPalindrome(char * s){
    int len = strlen(s);
    int i = 0, j = len - 1;
    while (i < j) {
        while (i < j && !isalnum(s[i])) i++;
        while (i < j && !isalnum(s[j])) j--;
        if (tolower(s[i]) != tolower(s[j])) return false;
        i++; j--;
    }
    return true;
}
